420 FISHES. 



(9) The glosso-pharyngeal, arising from the sides of 



the medulla oblongata, entering the auditory 



capsule, ending in connection with the first of 



the functional gill-slits. 



(10) The vagus, arising by six ganglionated roots 



from the hind region of the medulla oblongata, 



innervating gills, stomach, heart, and other 



parts. 



The spinal cord lies in the cartilaginous neural canal 



above the vertebral column, is divided by deep dorsal and 



ventral fissures, and gives off numerous spinal nerves, 



formed as usual from the union of dorsal (sensory) and 



ventral (motor) roots. The first sixteen or eighteen nerves 



form the brachial plexus, converging and uniting in a trunk 



which supplies the pectoral fin. 



The sympathetic system consists of a longitudinal ganglion- 

 ated cord along each side of the vertebral column. The 

 ganglia of these cords are connefcted with the spinal nerves. 



Sense-Organs. 



(a) The Eyes (see p. 387). The iris has a beautifully 



fringed upper margin. 



(b) The Ears (see p. 386). The vestibule is connected 



with the surface by a delicate canal — the aque- 

 ductus vestibuli — a remnant of the original in- 

 vagination. Within the vestibule are calcareous 

 otolithic particles surrounded by a jelly. 

 {c) The Nasal sacs are cup-like cavities with plaited 



walls. 



(d) The Sensory tubes are best seen on the ventral 



surface, where they lie just under the skin, and 



open by minute pores. They seem to form a 



diffused tactile system. 



Alimentary System. — The mouth is a transverse aperture ; 



the teeth borne by the jaws are numerous, and those worn 



away in front are replaced by fresh teeth from behind ; 



naso-buccal grooves connect the nostrils with the corners of 



the mouth ; the spiracles or first gill-clefts, which open 



dorsally behind the eyes, communicate with the buccal 



cavity ; from the gullet five gill-clefts open ventrally on each 



